Method of coating partially acetylated paper with plasticized cellulose ester and resulting paper coated with a photographic emulsion



July 31, 196.2 cv J. MALM ET AL 3, 3

METHOD OF COATING PARTIALLY ACETYLATED PAPER WITH PLASTICIZED CELLULOSE ESTER AND RESULTING PAPER COATED WITH A PHOTOGRAPHIC EMULSION Filed Jan. 12, 1959 SILVERHALIDE EMULSION LAYER PAPER BASE 0F PARTIALLY AETYLATED CELLULOSE FIBERS IMPREGNATED WITH LOWER FATTY ACID ESTER 0F CELLULOSE AND PLASTICIZER Carl JIMalm LloydE. Herdle GeraldGGandy IN VEN TORY .A'TTORNE-YS This invention relates to a method of improving the physical properties of partially acetylated paper.

- A simplified flow diagram of the method is as follows:

Paper of partially acylated fibers Impregnated with a solution in lower alcohol of a lower fatty acid ester of cellulose and plasticizer Alcohol evaporated off from the paper Paper subjected to heat and pressure to impart a smooth finish Paper is ordinarily prepared from cellulose fibers such as wood pulp by applying a slurry of the fibers to the wire of a papermaking machine from which the thus formed paper is led eventually to calender rolls to impart a smooth, even finish thereto. To improve the characteristics of such paper, sizing agents may be applied either to the paper or to the fibers prior to their formation into paper. However, paper made from partially acetylated cellulose fibers often exhibits considerable resistance to sizing operations.

One object of our invention is to provide a partially acetylated paper useful for photographic purposes, the wet strength and fold values of which are comparable with, or better than, those of papers normally used as a photographic paper base. Another object of our invention is to provide a paper which is. highly resistant to the efiects of moisture and to change in dimensional stability. Other objects of our invention will appear herein. 7

We have found that paper having highly desirable characteristics may be obtained if paper is formed from pulp which has been partially aceylated so as to impart an acetyl content of 15-30% and that paper is treated with an alcohol solution of a cellulose ester and a plasticizer. The

drying is treated with an alcohol solution of cellulose ester and plasticizer and after subjecting to pressure such as squeeze rolls and evaporation of the alcohol the paper is subjected to heat and pressure to give a smooth finish to the paper. The prevent the paper from losing its opacity, a pigment such as titanium dioxide can be incorporated in the solution as described and claimed in U.S. application Ser. No. 786,431 of Malm and Gandy, filed of even date.

The accompanying drawing represents in symbolic form, photographic paper having a paper base in accordance with the invention.

Many processes for partially acetylating wood pulp fibers actually decrease their strength and, consequently,

paper prepared therefrom is less strong than that prepared from fibers which had not been acetylated. However, whether or not partial acetylation has decreased the strength of the pulp fibers to any appreciable extent the treatment of paper sheets prepared therefrom with an aliphatic alcohol solution of a cellulose ester and a plasticizer for the cellulose compound has a beneficial eiiect upon the properties of the paper.

The alcohols which are of value in this connection are those of 1-4 carbon atoms such as butyl, isobutyl, propyl, isopropyl, ethyl and methyl. These alcohols have substantially no swelling effect on the partially acetylated fibers which is of particular advantage as the paper fibers take up only a minimum of the alcohol solution. For instance, with some types of solvents as much as 4 parts of solution will be retained by the paper, whereas the retention of the alcohol solution by the fiber can be held to less than 1 part of solution per part of paper.

The treatment of paper with alcohol Solution of cellulose ester and plasticizer gives a paper through which water vapor will readily pass and also prevents much of the cockle efiect upon subsequent rewetting and drying of the paper. The treatment described gives a uniform distribution of the cellulose ester and plasticizer therefor throughsheets of paper of this type have good wet strength and fold characteristics and the mullen and other properties are greatly improved. The cellulose fiber employed in making the paper is wood pulp which has been partially acetylated such as by some method described in the prior artor by the method described in U.S. application Ser. No.- 786,045 of Herdle and Gandy, now abandoned, filed of even date, or in U.S. application Ser. No. 786,042 of Malm and Blanchard, now abandoned, filed of even date. Procedures for partially acetylating cellulose fiber are described in British Patent No. 367,312, U.S. application Ser. Nos. 469,624 and 469,846 of Richter et al., filed November 18, 1954, both now abandoned, and in an article entitled Efiect of Acetylation on Water-Binding Properties of Cellulose, in Industrial and Engineering Chemistry, volume 35, pages 1206-1210, November 1943. After the cellulose fibers have been partially acetylated they are formed into a sheet by any conventional papermaking procedure such as in a handsheet mold or on the wire of a paper machine. The paper thus prepared after out the paper. The cellulose ester composition readily adheres to the fibers because of its aifinity for partially acetylated material. The cellulose esters whose alcohol solutions are employed are preferably the butyrates and propionates of cellulose. A certain amount of acetyl will be tolerated but there should be present sufiicient propionyl or butyryl that the cellulose ester employed is readily soluble in hot alcohol. If the alcohol solution is only liquid at an elevated temperature, it is desirable to first heat the paper prior to subjecting it to treatment therewith. In the case of alcohols which are not readily compatible with water, such as the butyl alcohols, heating of the paper initially is desirable to remove moisture therefrom. For instance, the paper prior to treatment may be subjected to a temperature of at least 120 F., the upper temperature limit being governed in part by that which will act derogatorily upon the paper. The plasticizer used may be any plasticizer for the cellulose ester, it being employed in considerable proportion such as 20 to 75% of the cellulose ester-plasticizer mixture. Some plasticizers which are useful in this connection are dibutyl phthalate, dibutyl sebacate, dioctyl phthalate, dibutyl adipate, and the like.

The partially aceylated paper treated in accordance with out invention is one which has been prepared from wood pulp fibers having an acetyl content of 15-25%. If the partially esterified fibers used have other acyl groups therer iently carried out by immersing the paper in the alcohol solution'of cellulose ester and plasticizer such as by running it through a bath thereof. This procedure can be very conveniently carried out in a continuous manner wherein a roll of paper is continuously unwound, heated and passed into a bath of the alcohol solution and the paper is continuously withdrawn through squeeze rolls, the alcohol evaporated oil and the paper passed over hot calender rolls thereby subjecting it to heat andpressure to give a smooth finish which is stable to water wetting and redrying. As the paper is not swollen, the amount of solution left in the paper is less than 1 part per part of paper. Upon evaporation of the alcohol the amount of cellulose ester and plasticizer which is retained in paper of usual thickness and absorbency is ordinarily less than A part per part of paper and preferably on the order of A part per part of paper.

In the case of the use of ethyl alcohol the pick up of the alcohol solution by the paper is greater than with the higher alcohols such as those of 3 or 4 carbon atoms. The solution employed ordinarily contains approximately 25% of cellulose ester and plasticizer dissolved in the alcohol. However, this concentration is optional as the solution can be considerably more dilute and will give interesting results in that the physical properties of the paper will be markedly improved. On the other hand, the amounts of cellulose ester and plasticizer used can be considerably more.

The following example illustrates our invention.

Example 1 Paper having a weight of 20 pounds per 1000 sq. ft. was made from a bleached kraft pulp which had been acetylated to an acetyl content of approximately 20%. This paper was passed through a solution consisting of 75% of n-butyl alcohol, 12.5% of halfecond viscosity cellulose acetate butyr-ate (butyryl 35-39%, acetyl 12- 15%) and 12.5% of dibutyl phthalate. The paper was passed through squeeze rolls to remove liquid therefrom leaving approximately /2 part of solution per part (by weight) of pulp. The alcohol in the paper sheet was evaporated therefrom bya current of warm dry air and the sheet obtained was supercalendered at .140 F. using 4 nips. This procedure was repeated on a paper which had been prepared as described but in which 1% of melamine formaldehyde resin had been incorporated in the paper stock prior to its manufacture on the wire of the paper machine. The following table lists the difference in physical properties between the paper in each case'which had not been treated with an alcohol solution of cellulose ester and plasticizer and a paper which had been so treated. The paper in which the melamine formaldehyde resin had been incorporated is designated wet strength paper.

Wet Strength Paper Waterleaf Paper After Treatment Before Treatment After Treatment Before Treatment L Folds G 52 232 9 203 Wet Strength xpansion wet In the above table L refers to lengthwise and C to the crosswise measurements of the paper.

Example 2 Paper having a weight of 20 pounds per 1000 sq. ft. was made from a bleached kraft pulp which had been acetylated to an acetyl content of approximately 20% and was passed through a solution as indicated in the following table. The excess solution was removed with squeeze rolls leaving approximately solution based on the weight of the pulp. The alcohol was evaporated from the sheet and the sheet was supercalendered using 4 nips at 140 F. In one case where the paper was prepared from fiber which had been jordaned only, the results obtained were as follows:

Paper Wet Strength Solution:

Percent alcohol Percent Ester Percent Plastlcizer 84isobuty1. 10.0 cellulose acetate-butyrate.

6.0 Dibut'yl phthalate.

Before Treatment After Treatment O- Mullen Wet Strength Expiansion, wet

(mere 1 38% Butyryl and 12% Acetyl20scc. viscosity.

Paper Wet Strength Solution:

Percent Alcohol 90 isopropyl 90 Isobutyl- 80 isobutyl, 10

Ethyl. Percent Ester 5.0 Cellulose Acetate-butyratefi 8.0 Cell. Ace- 5.0 Cell. acetate propionate 1 tate-butyratefi Percent Plasticizer 5.0 Dibutyl phthalate 2.0 Dibutyl Phthalate.

Before After After After After Treat. Treat. Treat. Treat. Treat.

Tear

60 60 58 62 64 64 65 63 63 Mu1len 19 33 31 29 35 Wet Strength--- 11 18% 18% 17% 34 Expansion, wet 1.20 1.05 1.15 1. 06 1.00 Fold L 16 60 60 60 52 (M.I.T.) O 10 34 64 37 63 45% Propionyl and 3.0% Acetyl20 second viscosity. 38% Butyryl and 12% Acetyl20 second viscosity.

The paper prepared in accordance with our invention is useful for preparing photographic paper by applying a silver halide emulsion layer thereon particularly after the paper had first been coated with a baryta layer as is well known in the art. It is desirable in the case of photographic use that the paper he prepared from a bleached pulp. However, our invention also contemplates the use of the treatment described upon paper made from unbleached pulp, which paper is useful for wrapping materials for electrical insulation or in any case where moisture absorption, resistance to swelling or dimensional change by moisture is important.

We claim:

1. A method of preparing paper resistant to the effect of moisture which comprises impregnating paper essentially consisting of partially acylated cellulose fibers with a solution in lower alcohol of a mixture of lower fatty acid ester of cellulose and a plasticizer therefor, in such manner as to leave less than 1 part of solution per part of paper, evaporating off the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper.

2. A method of preparing paper resistant to the effect of moisture which comprises impregnating paper essentially consisting of partially acetylated cellulose fibers with a solution in a lower alcohol of a mixture of lower fatty acid ester of cellulose and a plasticizer therefor, in such manner as to leave less than 1 part of solution per part of paper, evaporating ofi the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper.

3. A method of preparing paper resistant to the effect of moisture which comprises impregnating paper essentially consisting of partially acetylated cellulose fibers with a solution in a lower alcohol of a propionic acid ester of cellulose and a plasticizer therefor, in such manner as to leave less than 1 part of solution per part of paper, evaporating off the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper. 7

4. A method of preparing paper resistant to the effect of moisture which comprises impregnating paper essentially consisting of partially acetylated cellulose fibers ti with a solution in a lower alcohol 'of a butyric acid ester of cellulose and a plasticizer therefor, in such manner as to leave less than 1 part of solution per part of paper, evaporating off the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper. 5. A method of preparing paper resistant to the effect of moisture which comprises impregnating paper essentially consisting of partially acetylated cellulose fibers with a solution in a butyl alcohol of a mixture of a lower fatty acid ester of cellulose and a plasticizer therefor, in such manner as to leave less than 1 part of solution per part of paper, evaporating off the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper.

6. A method of preparing paper resistant to the efiect of moisture which comprises impregnating paper essentially consisting of partially acetylated bleached kraft pulp with a solution in butyl alcohol of a butyric acid ester of cellulose and dibutyl phthalate as the plasticizer for the cellulose ester, passing the paper through squeeze rolls to remove liquid therefrom, thereby leaving approximately /2 part of solution per part of paper, evaporating off the alcohol therefrom and subjecting to heat and pressure to impart a smooth finish to the paper.

7. Photographic paper comprising a paper base essentially consisting of partially acylated cellulose fibers which have been impregnated with a lower alcohol solution of a lower fatty acid ester of cellulose and a plasticizer from which paper the alcohol had been evaporated off and heat and pressure had been applied thereto and a photographic silver halide emulsion layer.

References Qited in the file of this patent UNITED STATES PATENTS 2,103,640 Richter Dec. 28, 1937 2,186,957 Collings et al Jan. 16, 1940 2,227,494 Gold Jan. 7, 1941 2,287,348 Hayden June 23, 1942 2,351,174 Whitehead June 13, 1944 2,357,962 Leemann et al Sept. 12, 1944 2,814,617 Hagenbuch et al Nov. 26, 1957 2,955,958. Brown Oct. 11, 1960 

1. A METHOD OF PREPARING PAPER RESISTANT TO THE EFFECT OF MOISTURE WHICH COMPRISES IMPREGNATING PAPER ESSENTIALLY CONSISTING OF PARTIALLY ACYLATED CELLULOSE FIBERS WITH A SOLUTION IN LOWER ALCOHOL OF A MIXTURE OF LOWER FATTY ACID ESTER OF CELLULOSE AND A PLASTICIZER THEREFOR, IN SUC MANNER AS TO LEAVE LESS THAN 1 PART OF SOLUTION PER PART OF PAPER, EVAPORATING OFF THE ALCOHOL THEREFROM AND SUBJECTING TO HEAT AND PRESSURE TO IMPART A SMOOTH FINISH TO THE PAPER. 